Thermoplastic resin structure

ABSTRACT

The present invention provides a thermoplastic resin structure which has a three-layer structure of flexible skin layer/flexible foamed material layer/hard substrate layer wherein each of the layers comprises a thermoplastic resin capable of melt-adhesion with each other, and the flexible foamed material layer is formed by the injection foam molding method. The resin structure exhibits the capability of being easily recycled and, at the same time, can be produced at a low cost, which has not been achieved by a conventional structure using a cross-linked foamed sheet or a urethane foam, while maintaining the performance in appearance, cushioning, rigidity and the like, and thus markedly useful for application fields requiring high performance in cushioning, sound absorption, heat insulation and the like in automobiles, household electrical appliances, general industrial parts and the like.

This application is a 371 application of PCT/JP99/06974 filed Dec. 13,1999.

TECHNICAL FIELD

The present invention relates to a structure comprising a thermoplasticresin. More specifically, it relates to a thermoplastic resin structurehaving a three-layer structure of flexible skin layer/flexible foamedmaterial layer/hard substrate layer, which is excellent in cushioningand strength, and makes it possible to effectively reuse, i.e., recyclethe used articles and to reduce costs.

BACKGROUND ART

Known three-layer structures of flexible skin layer/flexible foamedmaterial layer/hard substrate layer are shown as follows.

Conventional technique 1: a structure which comprises a slash moldedproduct of polyvinyl chloride (hereinafter abbreviated as PVC) or apolyolefin thermoplastic elastomer (hereinafter abbreviated as TPO) as aflexible skin layer (hereinafter referred to as a skin layer), apolyurethane-foamed product as a flexible foamed material layer(hereinafter referred to as a foamed layer), and a polypropylenecomposite material or an injection-molded product of an ABS resin as ahard substrate layer (hereinafter referred to as a substrate layer).

Conventional technique 2: a structure which comprises a polypropylenecomposite material or an injection-molded product of an ABS resin as asubstrate layer, and a sheet of a two-layer structure obtained bylaminating a cross-linked foamed sheet of polypropylene or high densitypolyethylene as a foamed layer on a skin layer of PVC or TPO.

These structures have been used for automobile interior materials andhave contributed greatly to the industrial fields as having excellentappearance, cushioning it, and rigidity.

In the conventional technique 1, however, foamed polyurethane, i.e., athermosetting resin is used for the foamed layer, so that the skinlayer, the foamed layer and the substrate layer should be separated whenthe structure is reused, i.e., recycled. Further, it is difficult toreuse foamed polyurethane, and therefore, the structure is not suitablefor recycling which has been required worldwide in recent years.

The conventional technique 1 also has a disadvantage of high productioncost, caused by quite different facilities required in the respectivesteps of a slash molding step of a skin layer, an injection or injectionpress molding step of a substrate layer and a urethane discharge-foamingstep of a foamed layer.

In the conventional technique 2, a cross-linked foamed material is usedfor the foamed layer. When the three layers are recycled at the sametime, the cross-linked foamed sheet is not homogeneously molten withmaterials constituting the skin layer and the substrate layer. Theperformance of the structure is therefore reduced when used as arecycled material. That is, the structure has a difficulty in recycling.

The conventional technique 2 also has a disadvantage of high productioncost, caused by a long series of molding steps comprising a foamedsheet-molding step of a foamed layer, a step of laminating a skin layeron the foamed sheet, a step of pre-molding the resulting composite sheetby a vacuum molding method or a compress molding method, and a step ofcombining the resulting pre-molded product with a substrate layer tomold in a die by an injection or injection press molding method, and bythe poor yield in pre-molding of the expensive composite sheet.

Further, both conventional techniques 1 and 2 described above use anadhesive or a pressure-sensitive adhesive so that at least a part of therespective layers adhere to each other, which may also cause difficultyin recycling of the structures and high costs.

The problems of difficulty in recycling and a high production cost inthese conventional techniques are caused by that the layers,respectively having a good appearance, cushioning and rigidity, areproduced from quite different materials or by quite different processingmethods and combined. Such a structure may be superior in quality, butthe above problems cannot be solved.

An object of the present invention is to provide a thermoplastic resinstructure capable of being surely recycled and reducing costs whilemaintaining high performance in appearance, cushioning and rigidity,which has not been achieved by conventional techniques.

The present inventors have made intensive researches in order to obtaina thermoplastic resin structure capable of being surely recycled andreducing costs while maintaining high performance in appearance,cushioning and rigidity, which has not been achieved by conventionaltechniques. As a result, the inventors have found that a structurehaving a three-layer structure of a flexible skin layer, a flexiblefoamed material layer and a hard substrate layer, the respective layerscomprising related thermoplastic resins capable of melt adhesion witheach other, the flexible foamed material layer comprising an injectionfoam molded product, can be surely recycled and reduce costs, whereinthe skin layer and the substrate layer can be combined at the same timeof molding the foamed material layer, and this three-layer structure caneasily be molten and reused only by pulverizing without separating therespective layers, whereby the present invention has been completed.

SUMMARY OF THE INVENTION

The constitution of the present invention is as follows.

(1) A thermoplastic resin structure having a three-layer structure offlexible skin layer/flexible foamed material layer/hard substrate layer,wherein the respective layers comprise thermoplastic resins capable ofmelt adhesion with each other and the flexible foamed material layer isformed by an injection foam molding method.

(2) The thermoplastic resin structure as described in the item (1),wherein the flexible skin layer and the hard substrate layer in thethree-layer structure comprising the flexible skin layer, the flexiblefoamed material layer and the hard substrate layer are each thermallywelded or thermally fused with the thermoplastic resin constituting theflexible foamed material layer by heat and pressure in injection foammolding of the flexible foamed material layer.

(3) The thermoplastic resin structure as described in the item (1) or(2), wherein the flexible skin layer, the flexible foamed material layerand the hard substrate layer in the three-layer structure each comprisepolyolefin thermoplastic resins.

(4) The thermoplastic resin structure as described in any one of theitems (1) to (3), wherein the flexible foamed material layer has anaverage expansion coefficient of 1.2 to 10.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the surface of a box type structureequipped with a rib which is obtained in the example.

FIG. 2 is a perspective view of the back of the above structure.

FIG. 3 is a cross section of the above structure.

FIG. 4 is a cross section of a die used in the examples and thecomparative examples.

FIG. 5 is an illustration of a flexible skin layer 1 and a hardsubstrate layer 2 being set in the above die.

FIG. 6 is an illustration of a flexible foamed material layer(non-foamed) 3 a formed by clamping the die in FIG. 5 while leavingspace for charging a material for the flexible foamed layer, andinjecting the material.

FIG. 7 is an illustration of a flexible foamed material layer (foamed) 3b formed by shifting the position of the die shown in FIG. 6 at aprescribed distance, foaming the material for the flexible foamed layerand maintaining the foamed layer.

EXPLANATION OF CODES

1. Flexible skin layer

2. Hard substrate layer

3 a. Flexible foamed material layer (non-foamed)

3 b. Flexible foamed material layer (foamed)

4. Fixed die

5. Moving die

6. Gate

7. Nozzle of injection-molding machine

BEST MODE FOR CARRYING OUT THE INVENTION

A flexible skin material used for a flexible skin layer in the presentinvention is a film- or sheet-shaped molded product obtained by aninjection-molding method or a calender roll molding method, and it ismolded from a material capable of melt-adhesion with a flexible foamedmaterial layer. A thermoplastic elastomer can suitably be used as thematerial used for the above flexible skin layer.

The thermoplastic elastomer shows a rubber elasticity at roomtemperature and can be molded in the same manner as conventionalthermoplastic resins, and it may be completely cross-linked, partiallycross-linked and non-cross-linked such as IPN (interpenetrated network).Any type can be applied in the present invention. Examples of thethermoplastic elastomer used in the present invention include polyolefinthermoplastic elastomers, styrene thermoplastic elastomers, isoprenethermoplastic elastomers, amide thermoplastic elastomers, esterthermoplastic elastomers and vinyl chloride thermoplastic elastomers.

Among them, polyolefin thermoplastic elastomers are preferred from aviewpoint of weight saving of the thermoplastic resin structure. Processoil may be blended in order to elevate a flexibility of the polyolefinthermoplastic elastomer. A completely cross-linked or partiallycross-linked polyolefin thermoplastic elastomer may be blended with aperoxide and melt-kneaded, for example, in order to elevate a rubberelasticity of the above polyolefin thermoplastic elastomer.

The thermoplastic elastomer used as the flexible skin material in thepresent invention preferably has a flexural modulus of 500 MPa or less,more preferably 300 MPa or less at 23° C. Preferable is the elastomerhaving a melt flow rate (hereinafter abbreviated as MFR) of 0.1 g/10minutes or more based on the test condition 14 (test temperature: 230°C.; test load: 21.18N) of JIS K7210. A MFR of less than 0.1 g/10 minutesmay reduce the fluidity in molding, resulting in poor appearance of themolded product Band difficulty in molding a large-sized molded product.

If necessary, the above thermoplastic elastomer may be blended with across-linking agent such as organic peroxide, a lubricant, anantioxidant, a neutralizing agent, a pigment, a photo-stabilizer, aprocess oil such as a mineral oil and an antistatic agent which are usedfor conventional thermoplastic elastomers.

The thermoplastic elastomer used for the flexible skin material in thepresent invention is produced by a conventional method. For example, thepolyolefin thermoplastic elastomer is produced by the following method.A crystalline ethylene-propylene copolymer and an ethylene-propylenecopolymer rubber are blended by means of a tumbler, and melt-kneaded bymeans of a twin screw extruder (PCM-45 manufactured by Ikegai Tekko Co.,Ltd.) at a cylinder temperature set to 200° C. to obtain a pelletizedpolyolefin thermoplastic elastomer.

An example of the material used as the flexible skin material in thepresent invention may be a polyolef in thermoplastic elastomer (TPO) inthe case that all the three layers in the three-layer structure comprisepolyolef in resins. In the case that the whole three-layer structurecomprises a polyvinyl chloride resin, an example thereof may be a softpolyvinyl chloride resin which is a polyvinyl chloride thermoplasticelastomer.

A flexible foamed material used for the flexible foamed material layerin the present invention is preferably a material capable ofmelt-adhesion with the flexible skin layer and the hard substrate layer,which has a suitable fluidity for an injection foam molding method and aexpansion coefficient of 1.2 to 10 or more. Specifically, theabove-described thermoplastic elastomers as the flexible skin materialcan be used. In the case that the whole the three layer structurecomprises a polyolefin resin, the above polyolefin thermoplasticelastomer can be blended with a propylene-ethylene random copolymerhaving a crystalline melting point of 125 to 150° C. in order to elevatean adhesion property of the flexible foamed material layer comprisingthe polyolef in thermoplastic elastomer to the hard substrate layercomprising a polyolef in resin described later.

A foaming agent for the flexible foamed material layer in the presentinvention is not particularly limited and can be any foaming agentsconventionally used in a chemical foaming method or a gas foaming methoddescribed later. It may be known substances generating gas by chemicaldecomposition or volatile liquids which are used for plastics or rubber.Specifically, examples thereof include azodicarbonamide,dinitropentamethylenetetramine, p,p′-oxybisbenzenesulfonylhydrazide,p,p′-oxybisbenzenesulfonylsemicarbazide,N,N′-dimethyl-N,N′-dinitrosoterephthalamide, sodium hydrogencarbonate,trichloromonofluoromethane and dichlorodifluoromethane. Azodicarbonamideand dichlorodifluoro-methane are preferred. A typical amount of thefoaming agents added is 0.01 to 10 parts by weight in the case of thechemical foaming method, and 0.1 to 100 parts by weight in the case ofthe gas foaming method, based on 100 parts by weight of the abovethermoplastic elastomer.

The substrate used for the hard substrate layer in the present inventionis a molded product, which is molded by an injection molding method oran injection press molding method and comprises a material capable ofmelt-adhesion with the flexible foamed material layer. A preferablematerial used for the hard substrate is a thermoplastic hard resin, forexample.

Examples of the thermoplastic hard resin used in the present inventioninclude polyethylene resins such as low density polyethylene, linear lowdensity polyethylene and high density polyethylene; polypropylene resinssuch as crystalline propylene homopolymers, crystallinepropylene-ethylene random copolymers and crystalline propylene-ethyleneblock copolymers; polyolefin resins such as poly(4-methylpentene-1);polystyrene resins; acrylonitrile-styrene copolymer resins;acrylonitrile-butadiene-styrene copolymer resins; methacryl-styrenecopolymer resins; polyamide resins; polyethylene terephthalate resins;polybutylene terephthalate resins; and polycarbonate resins. Among them,the polypropylene resins are preferred because the thermoplastic resinstructure can be decreased in weight. The above polypropylene resinspreferably have an isotactic pentad ratio of 0.94 or more, morepreferably 0.96 or more and a crystalline melting point of 163 to 165°C. so that the thermoplastic resin structure can have a high rigidity.They also preferably have a MFR of 10 to 40 g/10 minutes so as toreadily form the molded product having a complicated shape and a smallwall thickness.

The thermoplastic hard resin used in the present invention preferablyhas a flexural modulus of 600 MPa or more, more preferably 800 MPa ormore at 23° C. Further, it has preferably a MFR of 5 g/10 minutes ormore. If the thermoplastic hard resin has a MFR of less than 5 g/10minutes, the fluidity in molding is reduced, resulting in poorappearance of the molded product and difficulty in molding a large-sizedmolded product.

If necessary, the thermoplastic hard resin used in the present inventionmay be blended with an inorganic filler such as talc, mica and glassfiber; a synthetic rubber which is compatible with the thermoplastichard resin; and publicly known antioxidant, neutralizing agent,lubricant, antistatic agent and pigment which are used for conventionalthermoplastic hard resins. The inorganic filler is preferably added tothe thermoplastic hard resin in an amount of 5 to 60% by weight, morepreferably 10 to 50% by weight and further preferably 15 to 40% byweight so that the thermoplastic resin structure has a high rigidity.

Examples of the material used for the hard substrate in the presentinvention include a talc-composite polypropylene resin and a glassfiber-composite polypropylene resin in the case that all the threelayers in the three-layer structure comprise a polyolefin resin. In thecase that the whole three-layer structure comprises a polyvinyl chlorideresin, an example thereof may be a hard polyvinyl chloride resin.

The thermoplastic resin structure of the present invention can beobtained by molding a hard substrate layer in advance by an injectionmolding method or an injection press molding method, then molding afilm- or sheet-shaped flexible skin layer by an extrusion molding methodor a calender roll molding method, disposing both layers oppositely in adie with a space provided therebetween, charging a flexible foamingmaterial into the space by the injection molding method or the injectionpress molding method and then expanding a cavity of the die to therebyfoam the above flexible foaming material. In this case, the flexibleskin layer and the hard substrate layer are each thermally welded orthermally fused with the material constituting the flexible foamedmaterial layer by heat and pressure in charging the flexible foamingmaterial.

A means for foaming the flexible foamed material layer in the presentinvention may be any of a chemical foaming method and a gas foamingmethod, and both the flexible skin layer and the hard substrate layercan preferably adhere on both outside faces of the foamed material layerby injection foam molding or injection press foam molding. Any foamingagent, regardless of the above-described kinds, may be used as long asit generates such an amount of gas as to achieve a prescribed averageexpansion coefficient. That is, it is required for the flexible foamedmaterial layer in the present invention to be produced by charging a diewith a molten thermoplastic elastomer for the flexible foamed materiallayer by an injection or injection press molding method and foaming itat a desired expansion coefficient.

The average expansion coefficient of the flexible foamed material layerin the present invention can be indicated by an approximate valueobtained by dividing a volume of the foamed material layer in theproduct by a volume of a foaming thermoplastic elastomer charged intothe space of a die. Specifically, when 200 ml of the foaming moltenthermoplastic elastomer is charged to fill a space of 600 ml, theaverage expansion coefficient is 3 (=600 ml÷200 ml). However, theinjection foam molding method is characterized in that an expansioncoefficient is one, i.e., the elastomer is non-foamed or scarcelyfoamed, where a cavity is not expanded. Accordingly, the averageexpansion coefficient should be calculated excluding the part where thecavity is not expanded from a volume of the charged thermoplasticelastomer and a volume of the foamed material layer, respectively.

Specifically, assuming that a part where the cavity is not expanded hasa volume of 50 ml in the molded article, the above-mentioned equation iscalculated as follows.

(600−50) ml÷(200−50) ml=3.666 . . .

Thus, the average expansion coefficient is about 3.7.

On the assumption of the matter described above, the flexible foamedmaterial layer in the present invention preferably has an averageexpansion coefficient of 1.2 to 10, more preferably 1.5 to 8, which mayvary depending on parts of the foamed material layer according to theproduct shape or a dispersion of the foaming agent in the thermoplasticelastomer and a heat conduction of the foaming molten thermoplasticelastomer. If the flexible foamed material layer has an averageexpansion coefficient of less than 1.2, the layer feels hard even if thesoft material is used. If the average expansion coefficient exceeds 10,the restoring force is reduced. The good cushioning is not obtained ineither case.

EXAMPLES

The present invention shall further be explained in detail withreference to examples, but by no means limited thereto.

The followings are materials, an injection molding machine and a dieused in the following examples and comparative examples.

1) Flexible Skin Layer Material A

100 parts by weight of a crystalline propylene-ethylene block copolymer(ethylene content: 11.0% by weight), 230 parts by weight of anethylene-propylene-ethylidenenorbornene copolymer rubber (EPDM; brandname: EP57P manufactured by JSR Corporation) and 65 parts by weight of aprocess oil (brand name: DI Process Oil PW380 manufactured by IdemitsuKosan Co., Ltd.) were mixed, and the mixture was extruded and pelletizedto obtain a polyolefin thermoplastic elastomer (TPO) having a MFR of 0.5g/10 minutes. This TPO was formed into a film having a wall thickness of0.5 mm by means of a T-die extruder, thus giving a sheet-shaped flexibleskin layer material A having a hardness of 74 as determined according toa hardness test A of JIS K6301.

2) Flexible Skin Layer Material B

A polyolefin thermoplastic elastomer (brand name: NEWCON NNT2005manufactured by Chisso Corporation) having a MFR of 1.3 g/10 minutes wasformed into a film having a wall thickness of 0.5 mm by means of a T-dieextruder, thus giving a sheet-shaped flexible skin layer material Bhaving a hardness of 85 as determined according to the hardness test Aof JIS K6301.

3) Flexible Skin Layer Material C

100 parts by weight of a vinyl chloride polymer (average polymerizationdegree: 1,000) was mixed with 65 parts by weight of a plasticizer (DOP),and the mixture was formed into a film having a wall thickness of 0.5 mmby means of a calender roll apparatus, thus giving a sheet-shapedflexible skin layer material C having a hardness of 75 as determinedaccording to the hardness test A of JIS K6301.

4) Flexible Foamed Layer Material

100 parts by weight of a crystalline propylene-ethylene block copolymer(ethylene content: 11.0% by weight) was mixed with 200 parts by weightof low density polyethylene (brand name: Suntec-LD L-1850A manufacturedby Asahi Chemical Industry Co., Ltd.) and 200 parts by weight of anethylene-propylene copolymer rubber (EPR; brand name: TAFMER P0080Kmanufactured by Mitsui Chemical, Inc.), and the mixture was pelletizedto obtain a flexible material having a MFR of 18 g/10 minutes and ahardness of 87 as determined according to the hardness test A of JISK6301. 94% by weight of this flexible material was blended with 6% byweight of a foaming agent masterbatch (brand name: Chisso PolyproXKP1310W manufactured by Chisso Corporation) prepared by blending 20% byweight of azodicarbonamide (ADCA) with 80% by weight of a crystallinepropylene-ethylene-butene-1 random copolymer (ethylene content: 4.5% byweight; butene-1 content: 2.5% by weight) having a MFR of 6 g/10minutes, and they were mixed and stirred by means of a tumbler mixer toobtain a flexible foamed layer material (ADCA content: 1.2% by weight).

5) Hard Substrate Layer A

A polypropylene composite material for an automobile interior materialhaving a MFR of 20 g/10 minutes, which was prepared by blending 80% byweight of a crystalline propylene-ethylene block copolymer (ethylenecontent: 6.0% by weight) with 20% by weight of talc having an averageparticle diameter of 2 to 3 μm, was molded by means of ainjection-molding machine and a die, each described below, so that theresultant molding has a length of 410 mm, a width of 295 mm, a height of49 mm, and a wall thickness of 3 mm in a top board part. A hole 10 mm indiameter was drilled at the gate position as a passage for the flexiblefoamed layer material, thus giving a hard substrate layer A.

6) Hard Substrate Layer B

A hard substrate layer B was obtained in the same manner as the hardsubstrate layer A, except using glass-fiber reinforced polypropylene(brand name: Chisso Polypro GCS20 manufactured by Chisso Corporation)having a MFR of 2 g/10 minutes which was prepared by blending 20% byweight of glass fiber with 80% by weight of a crystalline propylenehomopolymer.

7) Hard Substrate Layer C

A hard substrate layer C was obtained in the same manner as the hardsubstrate layer A, except using an ABS resin (brand name: Sevian-V VF512manufactured by Daicel Chemical Industries, Ltd.) having a MFR of 5 g/10minutes.

8) Injection-molding Machine

An injection-molding machine equipped with a ion cylinder having a screwdiameter of 90 mm and a clamp-controlling mechanism, and having amaximum clamping force of 650 T.

9) Die

A die for molding a box shown in FIG. 4, which is its equipped with arib and has a length of 410 mm and a width of 295 mm, in which a heightcan be varied in a range of 47 to 60 mm and a wall thickness can bevaried in a range of 1 to 14 mm.

Example 1

The materials and the molding apparatus described above were used tocarry out the following example. The results thereof are shown in Table1.

The flexible skin layer material A having a wall thickness of 0.5 mm wascut according to a form of a die top face to obtain a flexible skinmaterial layer A1, which was fit on a moving die 5 of theabove-described die, wherein a height was adjusted to 51.5 mm and a wallthickness in the top board part was adjusted to 5.5 mm. Further, thehard substrate layer A2 having a wall thickness of 3 mm in the top boardpart, which was molded in advance, was fit on a fixed die 4 (See FIG.5). Next, these dies were clamped, and a flexible foamed layer materialwas injected into a space of 2 mm between the flexible skin layer A1 andthe hard substrate layer A2 to form a flexible foamed material layer(non-foamed) 3 a having a wall thickness of 2 mm (See FIG. 6). Afterprimary cooling for 2 seconds, the moving die 5 was shifted so that awall thickness was adjusted to 9.5 mm in the top board part, and theflexible foamed layer material was foamed simultaneously with shift ofthe moving die 5 to form a flexible foamed material layer (foamed) 3 b(See FIG. 7). Thereafter, secondary cooling was carried out for 60seconds while maintaining the position of the die (FIG. 7), and then amolded product was taken out. In the molded product taken out, theflexible skin layer A1 having a wall thickness of 0.5 mm, the flexiblefoamed material layer (foamed) 3 b having a wall thickness of 6 mm andthe hard substrate layer A2 having a wall thickness of 3 mm firmlyadhered to each other, and the flexible foamed material layer (foamed;average expansion coefficient=726 ml÷242 ml=3.0) 3 b maintained asufficient cushioning. Further, this molded product has the three-layerstructure comprising materials of the same kind only, without using anyadhesive or pressure-sensitive adhesive, so that it can be surelyrecycled.

Example 2

Molding was carried out in the same manner as in Example 1, except usingthe flexible skin layer material B for the skin layer and the hardsubstrate layer B2 as the substrate layer. The results thereof are shownin Table 1. In the molded product taken out, the flexible skin layer B1having a wall thickness of 0.5 mm, the flexible foamed material layer(foamed) 3 b having a wall thickness of 6 mm and the hard substratelayer B2 having a wall thickness of 3 mm firmly adhered to each other,and the flexible foamed material layer (foamed; average expansioncoefficient=3.0) 3 b maintained a sufficient cushioning. Further, thismolded product has the three-layer structure comprising materials of thesame kind only, without using any adhesive or pressure-sensitiveadhesive, so that it can be surely recycled.

Comparative Example 1

Molding was carried out in the same manner as in Example 1, except usingthe flexible skin layer material C for the skin layer. The resultsthereof are shown in Table 1. In the molded product taken out, theflexible skin layer C1 having a wall thickness of 0.5 mm and theflexible foamed material layer (foamed) 3 b having a wall thickness of 6mm did not adhere to each other and were readily peeled off from an endpart of the molded product. Further, the flexible skin layer C1 at thegate was broken by melting, resulting in a notably damaged appearance ofthe flexible skin layer C1.

Comparative Example 2

Molding was carried out in the same manner as in Example 2, except usingthe hard substrate layer C2 as the substrate layer. The results thereofare shown in Table 1. In the molded product taken out, the flexible skinlayer B1 having a wall thickness of 0.5 mm and the flexible foamedmaterial layer (foamed) 3 b having a wall thickness of 6 mm firmlyadhered to each other, but the above flexible foamed material layer(foamed). 3 b and the hard substrate layer C2 having a wall thickness of3 mm did not adhere to each other and were readily peeled off from anend part of the molded product.

TABLE 1 Comparative Example Example 1 2 1 2 Skin layer Flexible skinlayer Used — — — material A Flexible skin layer — Used — Used material BFlexible skin layer — — Used — material C Foamed Flexible foamed layerUsed Used Used Used layer material Substrate Hard substrate layer A Used— Used — layer Hard substrate layer B — Used — — Hard substrate layer C— — — Used Results Adhesion of skin layer G G N G to foamed layerAdhesion of foamed layer G G G N to substrate layer Surface cushioning GG N to G G

Remark: As the codes for the results, G represents “good”, and Nrepresents “not good”.

EFFECTS OF THE INVENTION

The present invention can provide a three-layer structure of athermoplastic resin comprising a flexible skin layer, a flexible foamedmaterial layer and a hard substrate layer, and capable of being readilyrecycled. Accordingly, it is very useful for application fieldsrequiring high performance in cushioning, sound absorption, heatinsulation and the like in automobiles, home electric appliances,general industrial parts and the like.

What is claimed is:
 1. A thermoplastic resin structure having athree-layer structure of flexible skin layer/flexible foamed materiallayer/hard substrate layer, wherein the respective layers comprisethermoplastic resins capable of melt adhesion with each other and theflexible foamed material layer is formed by an injection foam moldingmethod, in which the flexible skin layer and the hard substrate layerare each thermally welded or thermally fused with the thermoplasticresin constituting the flexible foamed material layer by heat andpressure in injection foam molding of the flexible foamed materiallayer.
 2. The thermoplastic resin structure as claimed in claim 1,wherein the flexible skin layer, the flexible foamed material layer andthe hard substrate layer in the three-layer structure each comprisepolyolefin thermoplastic resins.
 3. The thermoplastic resin structure asclaimed in claim 1, wherein the flexible foamed material layer has anaverage expansion coefficient of 1.2 to
 10. 4. The thermoplastic resinstructure as claimed in claim 2, wherein the flexible foamed materiallayer has an average expansion coefficient of 1.2 to
 10. 5. Thethermoplastic resin structure as claimed in claim 1, wherein theflexible foamed material layer is formed by an injection foam moldingmethod in which a flexible foaming material is foamed by expanding acavity of a die.
 6. The thermoplastic resin structure as claimed inclaim 2, wherein the flexible foamed material layer is formed by aninjection foam molding method in which a flexible foaming material isfoamed by expanding a cavity of a die.
 7. The thermoplastic resinstructure as claimed in claim 3, wherein the flexible foamed materiallayer is formed by an injection foam molding method in which a flexiblefoaming material is foamed by expanding a cavity of a die.
 8. Thethermoplastic resin structure as claimed in claim 4, wherein theflexible foamed material layer is formed by an injection foam moldingmethod in which a flexible foaming material is foamed by expanding acavity of a die.